Molecular analysis of six Rhynchospio Hartman, 1936 species (Annelida: Spionidae) with comments on the evolution of brooding within the group

Abstract

Rhynchospio Hartman, 1936 is a small group of spionid polychaetes currently comprising ten described species distributed mainly in the Pacific. Five species examined to date are hermaphrodites producing spermatozoa with long nuclei, oocytes with thin and smooth envelopes, and dorsally brooding their offspring. Since our first molecular analysis of four Rhynchospio species, we have collected additional material from Northern Territory, Australia, and Oregon, USA. Herein, we describe the gamete and adult morphology of the newly collected material and use molecular analyses to provide new insight on the phylogenetic relationships of six Rhynchospio species. Adults of R. cf. foliosa from Oregon are hermaphrodites, but in contrast to other Rhynchospio, they produce spermatozoa with short nuclei (ect-aquasperm), oocytes with thick vesiculate envelopes, and likely have a holopelagic larval development. Analysis of four gene fragments, comprising mitochondrial 16S rDNA, and nuclear 18S, 28S rDNA, and Histone 3 (2516 bp in total) showed Rhynchospio to be a monophyletic group, with R. cf. foliosa being a distant sister to the five other species. Rhynchospio cf. foliosa was closer to M. arctia having ect-aquasperm and vesiculate thick-envelop oocytes (p = 14.40%) than to Spioninae members B. proboscidea and P. elegans, having introsperm and oocytes with thin and smooth envelopes (p = 15.39 and 16.54%, respectively). We hypothesize that brooding might have evolved from free-spawning inside the Rhynchospio clade, but this hypothesis should be tested in a future analysis.

Morphological analysis of Rhynchospio aff. asiatica (Annelida: Spionidae) and comments on the phylogeny and reproduction of the family Spionidae

“…cf. foliosa have been recorded, molecular data are only available for seven species (Radashevsky et al, 2014(Radashevsky et al, , 2016aSimon et al, 2019b; this study), and the phylogenetic placements of the other six species (i.e., R . asiatica , R .…”

“…Types of larval development (i.e., Pla: planktotrophic; Lec: lecithotrophic; and Dir: direct development). The morphological groups were created by the authors in this study and the other groups mentioned here were present on diff erent studies (Jamieson and Rouse, 1989;Blake and Arnofsky, 1999;Radashevsky et al, 2016aRadashevsky et al, , 2018Blake et al, 2020). 2).…”

Molecular identification and larval morphology of spionid polychaetes (Annelida, Spionidae) from northeastern Japan

“…To date, three Rhynchospio species, R. foliosa Imajima, 1991, R. gutaea (Ehlers, 1987, and R. tuberculata Imajima, 1991, have been recorded from Japan (Imajima 1991a). However, extensive morphological and molecular studies revealed the absence of records of R. glutaea from the northern Pacific Ocean (Radashevsky 2007;Radashevsky et al 2014Radashevsky et al , 2016a. Radashevsky et al (2014) also referred to R. arenicola Hartman, 1936, R. asiatica Chlebovisch, 1959, R. aff.…”

Searching for a Home Port in a Polyvectic World: Molecular Analysis and Global Biogeography of the Marine Worm Polydora hoplura (Annelida: Spionidae)

“…We used the set of genes originally chosen for phylogenetic analysis of Spionidae [ 27 , 81 ]. The 16S rDNA is the most variable among examined markers and has been proven to be highly suitable for molecular identification at the species level for spionids [ 26 , 27 , 81 , 82 , 83 , 84 , 85 , 86 ].…”

“…We used the set of genes originally chosen for phylogenetic analysis of Spionidae [ 27 , 81 ]. The 16S rDNA is the most variable among examined markers and has been proven to be highly suitable for molecular identification at the species level for spionids [ 26 , 27 , 81 , 82 , 83 , 84 , 85 , 86 ]. Our genetic analysis of 16S dataset, however, does not reveal strongly robust biogeographic patterns of P. hoplura populations worldwide, since haplotype analysis was not the primary objective of our study, nor were our analyzed sample sizes large enough to reveal the full extent of haplotype diversity in any one region.…”